The present invention relates to a roaming method to be performed, particularly when a mobile terminal moves or roams to a service area of a service provider with which the mobile terminal has no contract, and further relates to a mobile communication system which is capable of carrying out such a roaming method.
In the field of mobile communication, a plurality of service providers have been offering their services in different regions or areas, respectively. These service providers have been offering roaming services so as to allow a mobile terminal located in a service area of a service provider with which the mobile terminal has no contract, to receive a service similar to that offered in a service area of a service provider with which the mobile terminal has a particular contract.
As will later be described in detail, in the conventional roaming method, for performing an authentication process of a roaming terminal with efficiency, an authentication key of the roaming terminal is notified from a home network to a roamed network during an initial roaming terminal registration procedure. Thus, there has been a problem of security in the conventional roaming method in view of data leakage since the authentication key of the corresponding roaming terminal is known by the roamed network.
For solving the foregoing problem, a method has been proposed as disclosed in Japanese Unexamined Patent Publication No. 4-352525(352525/92). In this method, a roamed network, in response to a location registration request received from a roaming terminal, first produces a temporary authentication key for use in a roaming terminal registration procedure and sends it to a home network. The home network performs an authentication of the roaming terminal via the roamed network. The home network holds a temporary authentication key setting key which is the same as that held by the roaming terminal. After completion of the authentication of the roaming terminal, the home network enciphers the temporary authentication key using the setting key and sends the enciphered temporary authentication key to the roaming terminal via the roamed network. Then, the roaming terminal deciphers the enciphered temporary authentication key using the setting key so as to derive the temporary authentication key. After this, the temporary authentication key is used for an authentication process relative to the roamed network. In this manner, the roaming terminal registration procedure can be performed without revealing an authentication key of the roaming terminal to the roamed network.
As described above, in the conventional roaming method, it is necessary that the roaming terminal first sends the subscriber's number (MSN) to the roamed network for achieving the location registration request. Since the roaming terminal carries out a transmission by radio, the transmission may be subjected to interception so that secrecy of the roaming terminal can not be ensured.